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- Log ----------------------------------------------------------------- commit b923dd3de0acbf415cee193191250347b733fab8 Author: Arne Fitzenreiter arne_f@ipfire.org Date: Fri May 1 10:33:02 2020 +0200
kernel: backport "random: try to actively add entropy"
this backports https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/dr... to gather enough entropy for initialise the crng faster. Of some machines like the APU it will need forever if the machine only wait for entropy without doing anything else.
Signed-off-by: Arne Fitzenreiter arne_f@ipfire.org
-----------------------------------------------------------------------
Summary of changes: lfs/linux | 4 + .../linux-4.14.x-add_timer_setup_on_stack.patch | 18 +++ .../linux-random_try_to_actively_add_entropy.patch | 146 +++++++++++++++++++++ 3 files changed, 168 insertions(+) create mode 100644 src/patches/linux/linux-4.14.x-add_timer_setup_on_stack.patch create mode 100644 src/patches/linux/linux-random_try_to_actively_add_entropy.patch
Difference in files: diff --git a/lfs/linux b/lfs/linux index 3651e120c..847abcbae 100644 --- a/lfs/linux +++ b/lfs/linux @@ -143,6 +143,10 @@ $(TARGET) : $(patsubst %,$(DIR_DL)/%,$(objects)) # Fix uevent PHYSDEVDRIVER cd $(DIR_APP) && patch -Np1 < $(DIR_SRC)/src/patches/linux/linux-2.6.32.27_mcs7830-fix-driver-name.patch
+ # Active try to add entropy if the kernel wait for it + cd $(DIR_APP) && patch -Np1 < $(DIR_SRC)/src/patches/linux/linux-random_try_to_actively_add_entropy.patch + cd $(DIR_APP) && patch -Np1 < $(DIR_SRC)/src/patches/linux/linux-4.14.x-add_timer_setup_on_stack.patch + ifeq "$(KCFG)" "-kirkwood" cd $(DIR_APP) && patch -Np1 < $(DIR_SRC)/src/patches/linux/linux-4.14.40-kirkwood-dtb.patch endif diff --git a/src/patches/linux/linux-4.14.x-add_timer_setup_on_stack.patch b/src/patches/linux/linux-4.14.x-add_timer_setup_on_stack.patch new file mode 100644 index 000000000..744dbe570 --- /dev/null +++ b/src/patches/linux/linux-4.14.x-add_timer_setup_on_stack.patch @@ -0,0 +1,18 @@ +diff -Naur linux-4.14.173.org/include/linux/timer.h linux-4.14.173/include/linux/timer.h +--- linux-4.14.173.org/include/linux/timer.h 2020-03-11 18:03:09.000000000 +0100 ++++ linux-4.14.173/include/linux/timer.h 2020-04-30 19:30:13.956596003 +0200 +@@ -180,6 +180,14 @@ + (TIMER_DATA_TYPE)timer, flags); + } + ++static inline void timer_setup_on_stack(struct timer_list *timer, ++ void (*callback)(struct timer_list *), ++ unsigned int flags) ++{ ++ __setup_timer_on_stack(timer, (TIMER_FUNC_TYPE)callback, ++ (TIMER_DATA_TYPE)timer, flags); ++} ++ + #define from_timer(var, callback_timer, timer_fieldname) \ + container_of(callback_timer, typeof(*var), timer_fieldname) + diff --git a/src/patches/linux/linux-random_try_to_actively_add_entropy.patch b/src/patches/linux/linux-random_try_to_actively_add_entropy.patch new file mode 100644 index 000000000..15d4319db --- /dev/null +++ b/src/patches/linux/linux-random_try_to_actively_add_entropy.patch @@ -0,0 +1,146 @@ +From 50ee7529ec4500c88f8664560770a7a1b65db72b Mon Sep 17 00:00:00 2001 +From: Linus Torvalds torvalds@linux-foundation.org +Date: Sat, 28 Sep 2019 16:53:52 -0700 +Subject: random: try to actively add entropy rather than passively wait for it + +For 5.3 we had to revert a nice ext4 IO pattern improvement, because it +caused a bootup regression due to lack of entropy at bootup together +with arguably broken user space that was asking for secure random +numbers when it really didn't need to. + +See commit 72dbcf721566 (Revert "ext4: make __ext4_get_inode_loc plug"). + +This aims to solve the issue by actively generating entropy noise using +the CPU cycle counter when waiting for the random number generator to +initialize. This only works when you have a high-frequency time stamp +counter available, but that's the case on all modern x86 CPU's, and on +most other modern CPU's too. + +What we do is to generate jitter entropy from the CPU cycle counter +under a somewhat complex load: calling the scheduler while also +guaranteeing a certain amount of timing noise by also triggering a +timer. + +I'm sure we can tweak this, and that people will want to look at other +alternatives, but there's been a number of papers written on jitter +entropy, and this should really be fairly conservative by crediting one +bit of entropy for every timer-induced jump in the cycle counter. Not +because the timer itself would be all that unpredictable, but because +the interaction between the timer and the loop is going to be. + +Even if (and perhaps particularly if) the timer actually happens on +another CPU, the cacheline interaction between the loop that reads the +cycle counter and the timer itself firing is going to add perturbations +to the cycle counter values that get mixed into the entropy pool. + +As Thomas pointed out, with a modern out-of-order CPU, even quite simple +loops show a fair amount of hard-to-predict timing variability even in +the absense of external interrupts. But this tries to take that further +by actually having a fairly complex interaction. + +This is not going to solve the entropy issue for architectures that have +no CPU cycle counter, but it's not clear how (and if) that is solvable, +and the hardware in question is largely starting to be irrelevant. And +by doing this we can at least avoid some of the even more contentious +approaches (like making the entropy waiting time out in order to avoid +the possibly unbounded waiting). + +Cc: Ahmed Darwish darwish.07@gmail.com +Cc: Thomas Gleixner tglx@linutronix.de +Cc: Theodore Ts'o tytso@mit.edu +Cc: Nicholas Mc Guire hofrat@opentech.at +Cc: Andy Lutomirski luto@kernel.org +Cc: Kees Cook keescook@chromium.org +Cc: Willy Tarreau w@1wt.eu +Cc: Alexander E. Patrakov patrakov@gmail.com +Cc: Lennart Poettering mzxreary@0pointer.de +Signed-off-by: Linus Torvalds torvalds@linux-foundation.org +--- + drivers/char/random.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++- + 1 file changed, 61 insertions(+), 1 deletion(-) + +(limited to 'drivers/char/random.c') + +diff --git a/drivers/char/random.c b/drivers/char/random.c +index 5d5ea4ce1442..2fda6166c1dd 100644 +--- a/drivers/char/random.c ++++ b/drivers/char/random.c +@@ -1731,6 +1731,56 @@ void get_random_bytes(void *buf, int nbytes) + } + EXPORT_SYMBOL(get_random_bytes); + ++ ++/* ++ * Each time the timer fires, we expect that we got an unpredictable ++ * jump in the cycle counter. Even if the timer is running on another ++ * CPU, the timer activity will be touching the stack of the CPU that is ++ * generating entropy.. ++ * ++ * Note that we don't re-arm the timer in the timer itself - we are ++ * happy to be scheduled away, since that just makes the load more ++ * complex, but we do not want the timer to keep ticking unless the ++ * entropy loop is running. ++ * ++ * So the re-arming always happens in the entropy loop itself. ++ */ ++static void entropy_timer(struct timer_list *t) ++{ ++ credit_entropy_bits(&input_pool, 1); ++} ++ ++/* ++ * If we have an actual cycle counter, see if we can ++ * generate enough entropy with timing noise ++ */ ++static void try_to_generate_entropy(void) ++{ ++ struct { ++ unsigned long now; ++ struct timer_list timer; ++ } stack; ++ ++ stack.now = random_get_entropy(); ++ ++ /* Slow counter - or none. Don't even bother */ ++ if (stack.now == random_get_entropy()) ++ return; ++ ++ timer_setup_on_stack(&stack.timer, entropy_timer, 0); ++ while (!crng_ready()) { ++ if (!timer_pending(&stack.timer)) ++ mod_timer(&stack.timer, jiffies+1); ++ mix_pool_bytes(&input_pool, &stack.now, sizeof(stack.now)); ++ schedule(); ++ stack.now = random_get_entropy(); ++ } ++ ++ del_timer_sync(&stack.timer); ++ destroy_timer_on_stack(&stack.timer); ++ mix_pool_bytes(&input_pool, &stack.now, sizeof(stack.now)); ++} ++ + /* + * Wait for the urandom pool to be seeded and thus guaranteed to supply + * cryptographically secure random numbers. This applies to: the /dev/urandom +@@ -1745,7 +1795,17 @@ int wait_for_random_bytes(void) + { + if (likely(crng_ready())) + return 0; +- return wait_event_interruptible(crng_init_wait, crng_ready()); ++ ++ do { ++ int ret; ++ ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ); ++ if (ret) ++ return ret > 0 ? 0 : ret; ++ ++ try_to_generate_entropy(); ++ } while (!crng_ready()); ++ ++ return 0; + } + EXPORT_SYMBOL(wait_for_random_bytes); + +-- +cgit 1.2-0.3.lf.el7 +
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